The invention relates to a process and mechanism for determining the effective air temperature in at least one pneumatic tire of a vehicle by a mechanism which measures the temperature in proximity of the interior side of the rim of the respective vehicle wheel.
A process and mechanism for this type of temperature sensing are known in vehicle tire air pressure monitoring devices or vehicle tire air pressure control devices.
For example, DE-OS 35 39 489 shows a process for the monitoring of the vehicle tire air pressure, wherein the determined tire air pressure value of one of the pneumatic vehicle tires is compared with desired tire air pressure value which is a function of the air temperature in the respective pneumatic tire of the vehicle.
In all previously known vehicle tire air pressure monitoring devices and vehicle tire air pressure control devices utilizing air temperature, the temperature is measured in proximity of the interior side of the rim of the respective vehicle wheel by means of a temperature sensor arranged thereat. However, this method of determining the tire air pressure is very inexact, since the temperature measured by means of the temperature sensor arranged at the interior side of the rim of the respective vehicle wheel is falsified by the heat transmission from the exterior side of the rim to the interior side of the rim of the respective vehicle wheel. This heat transmission is a function of the temperature at the exterior side of the rim of the respective vehicle wheel which, in turn, is determined by the respective outside temperature; (the respective ambient temperature of the vehicle) and by the braking heat radiated by the pertaining vehicle brake disk or vehicle brake drum.
It is therefore an object of the invention to provide a process as well as a mechanism for determining the effective air temperature in at least one of the pneumatic tires of a vehicle to avoid the above inexact temperature sensing.
According to the invention, this object is achieved in that, in addition to the temperature in proximity of the interior side of the rim of the respective vehicle wheel, the temperature in the immediate environment of a vehicle brake disk or vehicle brake drum, as well as the temperature in the immediate environment of the vehicle are measured. The effective air temperature in the respective pneumatic vehicle tire is calculated from these measured values of the temperature in the proximity of the interior side of the rim, for the temperature in the immediate environment of a vehicle brake disk or vehicle brake drum, and of the temperature in the direct environment of the vehicle.
The value of the effective air temperature in the pneumatic vehicle tire (determined in this manner) is independent of the outside temperature and thus of the temperature in the immediate environment of the vehicle and is also independent of the heat quantity which is radiated by the vehicle brake disk or vehicle brake drum assigned to the respective vehicle wheel. Thus the temperature measured by the temperature sensor arranged at the interior side of the rim which is compensated by the outside temperature and the heat radiation of the Pertaining vehicle brake disk or vehicle brake drum is a more exact temperature.
Preferably, the effective air temperature in the pneumatic vehicle tire is determined according to the following mathematical formula: EQU T.sub.RLeff =T.sub.I -f.sub.1 (T.sub.UB)+f.sub.2 (T.sub.UF)
wherein
T.sub.RLeff =effective air temperature in the pneumatic vehicle tire PA1 T.sub.I =temperature in proximity of the interior side of the rim of the respective vehicle wheel PA1 f.sub.l =first mathematical function of the temperature in the immediate environment of a vehicle brake disk or vehicle brake drum PA1 T.sub.UB =temperature in the immediate environment of a vehicle brake disk or vehicle brake drum PA1 f.sub.2 =second mathematical function of the temperature in the immediate environment of the vehicle PA1 T.sub.UF =temperature in the immediate environment of the vehicle
A device for carrying out the above-described process, includes a first temperature sensor arranged at the interior side of the rim of the respective vehicle wheel, a second temperature sensor in the immediate environment of a vehicle brake disk or vehicle brake drum, a third temperature sensor for detecting the ambient temperature of the vehicle and a computing unit for calculating the effective air temperature in the respective pneumatic vehicle tire in accordance with the above formula and outputs from the aforementioned three temperature sensors.
The three temperature sensors are preferably constructed as analog sensors.
According to a further development of the invention, the thermal time constants and the error tolerances of the three temperature sensors are at least almost identical. In the case of temperature sensors that are selected in this manner, the calculation of the effective air temperature in the pneumatic vehicle tire can take place in a very simple manner.
According to a further development of the invention, the second temperature sensor and the third temperature sensor are arranged on the same vehicle side.
The second temperature sensor is preferably arranged in the wheel housing of a vehicle front wheel. In the case of this arrangement of the second temperature sensor, the temperature in the immediate environment of a vehicle brake disk or vehicle brake drum can be detected very well.
The second temperature sensor is preferably arranged at the vehicle such that the temperature proportion of the temperature in proximity of the interior side of the rim of the respective vehicle wheel, which is a result of the heat radiation of the vehicle brake disk or vehicle brake drum, is completely compensated by the value of the difference of the temperature in the immediate environment of the vehicle brake disk or vehicle brake drum, minus the temperature in the immediate environment of the vehicle. In the case of this type of an arrangement of the second temperature sensor at the vehicle, the effective air temperature of a pneumatic vehicle tire can be determined by the subtraction of the temperature in the immediate environment of a vehicle brake disk (or vehicle brake drum) from the addition of the temperature in the immediate environment of the vehicle and the value to the temperature in proximity of the interior side of the rim of the respective vehicle wheel.
It has also been proven to be advantageous for the third temperature sensor to be arranged in one of the front or the rear lateral bumper parts. This arrangement ensures that the third temperature sensor is protected from rain and dirty water, direct sun radiation as well as the heat radiation of the internal-combustion engine of the vehicle. Additionally, the sensor is accessible to the air stream.
The above-described process as well as the above-described device are preferably used for a vehicle tire air pressure monitoring devices or for a vehicle tire air pressure control devices.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.